1. Field of the Invention
The present invention relates to certain novel insecticides and to novel insecticidal compositions comprising, as the active ingredient thereof, an isovaleric acid ester bearing a substituent group in the .alpha.- or .beta.-position, said isovaleric acid ester having the structural formula [I]: ##STR7## wherein Z.sup.1 is hydrogen, ##STR8## Z.sup.2 is either ##STR9## when Z.sup.1 is hydrogen, or hydrogen when Z.sup.1 is either ##STR10## A, when Z.sup.1 is ##STR11## is cyano or ethynyl or, when Z.sup.1 is other than ##STR12## is hydrogen, cyano or ethynyl; X and Y which may be the same or different are chlorine or bromine.
The isovaleric acid ester substituted in the .alpha.- or .beta.-position as represented by the above structural formula [I] comprises the four types of substituted isovaleric acid esters which are designated by the following structural formulae [I-A], [I-B], [I-C] and [I-D], respectively: ##STR13##
The compounds [I-A], [I-B] and [I-C] are the novel compounds according to the invention.
2. Description of the Prior Art
Since the discovery of BHC and DDT, there has been great development of a wealth of different insecticides containing, as the active ingredient thereof, a variety of organophosphorus compounds, carbamates, chlorinated organic compounds, and many others, for farming and gardening applications, and the use of such insecticides has resulted in marked increases in crop yields, thus enabling a stabilized supply of crops without depending upon climatic conditions. However, this success has been more or less offset by the fact that such agricultural and horticultural insecticides not only have high toxicity to humans and domesticated animals, but also same display a great tendency towards environmental pollution. Thus, the chronic toxicity and accumulation of such poisons have become a major contemporary concern. Furthermore, in many geographical areas, agricultural pests such as green rice leafhoppers, plant hoppers, etc., have been acquiring resistance to the common pesticides comprising the organic phosphorus compounds or the carbamates and the development of substitutes for such chemicals today is a pressing need. Pyrethroid pesticides, such as allethrin, phthalthrin, resmethrin, furamethrin, pyrethrin, etc., which have heretofore been employed for the purpose of controlling household pests are not only low in toxicity to man and domestic animals, have excellent pesticidal activities and are fast-acting against noxious insects, but too are known for the fact that pests acquire resistance thereto only very rarely. However, because of their extremely low stability to light and their low residual activity, these compounds cannot be used as agricultural or horticultural pesticides to replace the organophosphorus or carbamate pesticides.
Under these circumstances, there have been certain developments in agricultural and horticultural pesticides which take advantage of the characteristics of pyrethroids, which characteristics are not possessed by the conventional agricultural pesticides.
Among the pesticides recently developed have been 3-phenoxybenzyl (+)-cis,trans-2,2-dimethyl-3-(2,2-dichlorovinyl)-cyclopropanecarboxylate [Permethrin, U.S. Pat. No. 4,024,163] which has the structural formula: ##STR14## and .alpha.-cyano-3-phenoxybenzyl .alpha.-(4-chlorophenyl)isovalerate [Fenvalerate, U.S. Pat. No. 3,996,244] which has the structural formula: ##STR15##
However, because of their high toxicity to fish, the applicability of these compounds is considerably restricted in geographical areas where, if used, they would contaminate the river water, etc.
Further, 3-phenoxybenzyl .alpha.-(2,2-dichlorovinyl)-isovalerate having the structural formula: ##STR16## and .alpha.-(allyl or 3,3-dimethylallyl)isovaleric acid esters having the following structural formulae: ##STR17## (wherein A' is hydrogen, alkynyl or cyano) are reported to have pesticidal activity against agricultural, horticultural and household pests [published, unexamined Japanese Patent Application No. 125723/1976 and U.S. Pat. No. 4,042,710]. However, none of such compounds displays a fully satisfactory pesticidal activity.